Actually, R134a is an HFC, not an HCFC, (no chlorine or bromine)and per the EPA has zero ozone depletion potential:
"Hydrofluorocarbon (HFC): a compound consisting of hydrogen, fluorine, and carbon
The HFCs are a class of replacements for CFCs. Because they do not contain chlorine or bromine, they do not deplete the ozone layer. All HFCs have an ozone depletion potential of 0. Some HFCs have high GWPs. HFCs are numbered according to a standard scheme. The National Oceanic and Atmospheric Administration provides more detailed information about HFCs on their web site."
Also, Methane gas, a hydrocarbon, is a demonstrated contributer to global warming. Again per the EPA
A hydrocarbon that is a greenhouse gas with a global warming potential most recently estimated at 21. (about 21 times the warming potential of carbon dioxide, but less than the warming potential of HFCs or HCFCs) Methane is produced through anaerobic (without oxygen) decomposition of waste in landfills, animal digestion, decomposition of animal wastes, production and distribution of natural gas and petroleum, coal production, and incomplete fossil fuel combustion. The atmospheric concentration of methane as been shown to be increasing at a rate of about 0.6 percent per year and the concentration of about 1.7 per million by volume (ppmv) is more than twice its pre-industrial value."